This invention is concerned with coating EPDM rubber membranes. More particularly, though not exclusively, this invention is concerned with a method for improving the adhesion of a coating to an EPDM rubber membrane.
A large proportion of the roofing market utilizes asphalt-based products, for example, modified bituminous rolls, as a base membrane or roofing membrane which is then topcoated with conventional roof mastics to improve durability (asphalt degradation), provide energy savings (white coating vs. black asphalt), reduce the fire rating and improve aesthetics. Such coatings are frequently referred to as xe2x80x9croof masticsxe2x80x9d although xe2x80x9ccoatingsxe2x80x9d as used herein includes any such thick coatings applied to a substantially horizontal surface such as, for example, a roof deck, to a substantially vertical surface such as, for example, a wall, or to other membrane surfaces.
EPDM (ethylene propylene diene monomer) rubber is also utilized in the roofing market as a roofing membrane. However, unlike the bituminous roofing membranes, EPDM roofing membranes have hitherto been difficult to topcoat with a mastic, due to poor adhesion between the mastic and EPDM rubber, particularly on flat or low slope roofs where ponding of rain water occurs. Even when the membrane surface has been cleaned and scrubbed with water or with a mild detergent and then rinsed with water immediately before application of the mastic, there is little or no measurable improvement in adhesion. Consequently, roofs covered with EPDM rubber tend not to be topcoated with a mastic and, therefore, fail to benefit from the improvements which a mastic topcoat can provide.
A coating system which displays good adhesion and superior resistance to blistering, especially when exposed to ponded water is disclosed in U.S. Pat. No. 5,059,456. This system relies upon the use of a water-based tiecoat between the membrane and the coating. The tiecoat consists of a water-insoluble latex polymer and multivalent metal ion, wherein the latex polymer comprises units such as would result from preparation from a monomer mixture comprising at least 20 weight %, based on the weight of the monomer mixture, of at least one hydrophobic monomer selected from the group consisting of (C4-C20)-alkyl methacrylates and (C8-C20)-alkyl acrylates, and from 3.0 weight % to 7.5 weight % of methacrylic acid, based on the weight of the monomer mixture, and where the latex polymer has a glass transition temperature of from xe2x88x9220xc2x0 C. to 5xc2x0 C., and where the molar ratio of the multivalent metal ion to the methacrylic acid in the latex polymer is from about 1:1 to about 0.375:1. The tiecoat is applied to a membrane before subsequent application of a coating. Though this system offers properties of adhesion and resistance to blistering which are superior to conventional mastic systems on bituminous membranes, there is no disclosure of coating EPDM rubber membranes.
It is an object of the present invention to provide a coating system which offers improved adhesion on EPDM rubber membranes, such as roofing membranes. Moreover, it is preferred if the above improvements in the quality of a coating system can be achieved with a system which does not essentially rely upon the use of a tiecoat between the membrane and mastic composition.
In accordance with the present invention, there is provided a method for improving the adhesion between a coating and an EPDM rubber membrane, which method comprises:
(A) treating a surface of an EPDM rubber membrane with an aqueous detergent composition; then
(B) rinsing said surface of said EPDM rubber membrane with water to remove said detergent composition; and then
(C) applying a coating composition to said rinsed surface of said EPDM rubber membrane,
wherein said aqueous detergent composition has a pH above 8 and comprises from 1 to 10% by weight phosphate and from 1 to 10% by weight silicate.
Surprisingly, it has been found that by pre-treating an EPDM rubber membrane with said detergent composition before applying a conventional coating composition, a synergistic improvement in adhesion between the membrane and coating can be achieved. The surprising advantages of the present invention may be measured for both coatings applied on newly laid membranes and coatings applied on old membranes which have been laid on roofs for an extended period of time.
Preferably, the membrane for application of the invention is an EPDM rubber membrane sold for roofing applications. Preferably, the roofing membrane lies over a flat or low slope roof.
The coating composition will preferably comprise a water-insoluble latex polymer binder, having a glass transition temperature of from xe2x88x9245xc2x0 C. to 5xc2x0 C. (as measured by the Fox equation), which is preferably acrylic or styrene/acrylic. In addition to the latex polymer, the composition will comprise at least one or more of the following components: pigments, extenders, dispersants, surfactants, coalescents, wetting agents, thickeners, rheology modifiers, drying retarders, plasticizers, biocides, mildewicides, defoamers, colorants, waxes, dirt pick-up retarders, adhesion promoters, zinc oxide and solid silica. The coating composition is preferably a mastic coating composition. The binder used in the mastic coating composition is preferably a commercially available binder useful for mastic applications, such as a binder selected from the group including Rhoplex EC-1791, Rhoplex 2019R and Rhoplex EC-2885 available from Rohm and Haas Company; Acronal NX 3550 available from BASF AG and DA26NA available from Dow. More preferably, the mastic binder is selected from the group including Rhoplex EC-1791, Rhoplex EC-2885 and Acronal NX 3550. Rhoplex EC-1791 is the most preferred mastic binder composition.
The aqueous detergent composition comprises from 1 to 10%, preferably 2 to 8%, more preferably 3 to 6%, by weight of said composition of a mono- or poly-phosphate or a mixture of such phosphates, preferably selected from the group consisting of trisodium phosphate, sodium tripolyphosphate and tripotassium phosphate. Trisodium phosphate is the most preferred. The aqueous detergent composition comprises from 1 to 10%, preferably 2 to 8%, more preferably 3 to 6%, by weight of said composition of a meta-, ortho- or para-silicate or a mixture of such silicates, preferably selected from the group consisting of sodium metasilicate and potassium metasilicate. Sodium metasilicate is the most preferred. The phosphates and silicates useful in the detergent composition are those commonly used in conventional detergent compositions, such as in dish-washing and clothes-washing detergents.
The aqueous detergent composition may also comprise other components typically found in aqueous detergent composition. For example, the composition may comprise up to 5%, preferably up to 2%, by weight of at least one compound selected from the group consisting of octylphenoxy polyethoxy ethanol, octyphenoxy polyethoxy ethylphosphate, polyethylene glycol and phosphoric acid.
The aqueous detergent composition has a pH of above 8, preferably a pH from 9 to 14, and most preferably a pH from 12 to 14.
The best results are obtained from the present invention when all the surface of the EPDM rubber membrane is contacted with the detergent composition. The detergent composition may be spread over the surface with the aid of a stiff brush. The detergent composition should preferably be left to stand in contact with the surface of the membrane for a short period of time. For example, though an improvement in adhesion of a coating may be measured when the detergent composition is left to treat the surface for less than 30 seconds, the best results are achieved when the detergent composition is allowed to contact the surface for at least 30 seconds. A contact time significantly over 30 seconds will tend not to lead to any significant further improvements in adhesion over a contact time of 30 seconds, though in practice contact times may be 10 to 30 minutes depending on the size of the roof and the speed of the operator. Permitting the detergent to dry on the surface before rinsing may not be detrimental to the method of the present invention, provided the surface is rinsed well afterwards to remove the detergent.
The best results are obtained from the present invention when rinsing of the surface of the EPDM rubber membrane with water removes substantially all of the detergent composition. High efficiency rinsing may involve the use of a stiff brush and/or the use of a high pressure hose. Typically, the high pressure hose will release rinse water at about 211 Kg cmxe2x88x922 (3000 psi).